Acids and Bases

Elective Chemistry, Form 4
Practical #1
Acid-Base Titration

THEORY

One common type of chemical reaction is acid-base neutralization. All neutralization reactions follow the same basic formula:

H⁺ + OH^- → H₂O

Acid + Base → Water

When acid and base have completely reacted and the solution is neutral (pH = 7), the end point or equivalence point has been reached. In order to determine the end point of a reaction, a process called titration is used. In titrations, acid is slowly added to base just until the solution has been  neutralized.

My boys just doin some chemistry.. Studs!

An indicator, which has no effect on the reaction, is added to the base to signal the pH of the solution.

(pH )         2       3       4       5      6      7      8      9       10      11

(Color)      Pink   Orange   Yellow      Green   Blue   Violet

Trials 1, 2, and 3

Good.. Better.. Best!

Titration is a very useful technique in a chemistry laboratory. For example, the unknown concentration of a base can be determined from a titration with an acid of known concentration.

Concentration = Amount of Substance (moles) / Volume of Solution (dm³)

In this particular experiment, hydrochloric acid, HCl will be titrated against ammonium, NH₃. The formula for this neutralization reaction is as follows:

NH_3(aq) + H₂O₍₁₎ → NH₄⁺_(aq) + OH^-_(aq)

NH₄⁺_(aq) + OH^-_(aq) + HCl_(aq) → H₂O_(l) + NH₄Cl_(aq)

OBJECTIVE

Determine the unknown concentration of a solution of NH₃ from a titration with 1.8M HCl.

METHODS

Perform three (3) trials of the following procedure:

1.) Using a plastic funnel, carefully add 1.8M HCl to the burrette.

2.) Record the starting burrette volume.

3.) Using a 100mL graduated cylinder, measure 20mL NH₃ into a 250mL beaker.

4.) Add 5-10 drops of Harris Indicator to the NH₃.

5.) Open the burrette stopcock so that acid flows in a slow steady stream into the beaker containing the NH₃ and indicator. Swirl the contents of the beaker as acid is added to ensure that it is thoroughly mixed.

6.) When the solution turns yellow, immediately close the burrette stopcock. Record the final burrette volume.

:) I am SO proud! (:

PS. The reason this is so impressive... These boys had never been in a chemistry lab before.